Juvenile idiopathic arthritis : disease consequences and treatment effects on muscle strength, gait and pain

Abstract

Juvenile idiopathic arthritis (JIA) may have a profound effect on the life of a child. Rheumatic diseases in children manifest mainly as synovitis, pain, stiffness, deformity, growth disturbances and fatigue. It is not uncommon to have reduced activity, lower aerobic endurance, and decreased muscle strength. The inflammatory process of the disease most often affects extremities and restriction of joint motion often occurs. Forty percent of the children with JIA report difficulty in daily activities. The aims of this thesis were to compare lower extremity strength and gait and to evaluate pain in children with JIA and children without musculoskeletal dysfunction.

Both a Hand Held Dynamometer (HHD) and an isokinetic dynamometer were used to test maximal isometric muscle strength. The maximal isometric plantar- and dorsiflexor strength evaluated with the two dynamometers were lower in the children with JIA than in the controls. In dynamic muscle actions, measured with the isokinetic dynamometer the controls were significantly stronger than the JIA group in shortening plantarflexor and in shortening and lengthening dorsiflexor actions.

Comparisons between action types showed larger lengthening torques than isometric or shortening, and comparisons between muscle groups showed all plantarflexor torques to be four to five times greater than dorsiflexor torque. Children with JIA walked with a slower velocity than healthy controls. After intraarticular corticosteroid injections (ICI) the children with JIA increased their speed. Difference in the vertical ground reaction forces at loading response and at terminal stance was observed between children with JIA and controls wherein the peaks observed in the normal ground reaction force are attenuated in the children with JIA. The results after treatment with ICI indicated increased knee and ankle flexion extension angles during walking. Hip extension moment at loading response and knee- and plantarflexion moment at preswing increased after treatment with ICI. Positive effects of treatment with ICI were observed during gait even in joints not injected.

The Pain-O-Meter word descriptors are a possible tool for assessment of sensory and affective dimension of pain in children age 616 yrs. The number of words, however known in small children was fewer and no difference in pain experience was observed between children with acute or chronic pain. Novelty data in this thesis are dynamic plantarflexor torque measured on children with JIA and assessment of ICI on gait. The clinical implications are numerous - weakness in almost all action types in plantar-and dorsiflexors indicates the importance of sthrength-training these muscle groups and the need to evaluate the muscle strength with a safe and objective method continuously. Three dimensional gait analyses provide information about gait such as joint angles, joint moments and power during walking which are impossible to quantify during a standard clinical medical examination.

The findings of lower walking velocity, muscle strength and joint moments in children of JIA indicate the importance of encouraging the children to participate in physical activities as much as possible to prevent a vicious circle with deteriorating fitness.